The invention relates to a rope drive element for driving synthetic fiber ropes, preferably for a rope drive of an elevator installation.
Rope drives of this type are used in materials handling, especially in mining and the construction of cranes and elevators, or on aerial cableways and similar installations. It is known that the function of such rope drives is based on the driving force being transferred to the section of rope which is in contact at any time with the rope drive element, e.g. the traction sheave, rope drum, or similar. As the rope runs over the traction sheave it is bent, which causes compensating movements of the strands of a multi-layer rope.
The tractive capacity of such traction systems is restricted to operating ranges with sufficient frictional engagement between the traction sheave and rope. For example, on a rope traction elevator at least the difference in weight between the counterweight and car must be compensated by the frictional force on the traction sheave. The torque must also be transferred from the traction sheave to the rope by frictional engagement. For this reason, rope drives are designed in such manner that there is always sufficient tractive capacity for the various hoisting situations, e.g. normal travel, emergency stopping, loading, and unloading. The range of frictional engagement is limited in essence by a minimum and maximum so-called allowable system coefficient of friction between the traction sheave and the rope passing over it.
To create the appropriate coefficient of friction on the traction sheave, on conventional traction sheaves shaped grooves, e.g. a V-groove or an undercut semicircular groove, are cut whose shape exerts a specific pressure on steel ropes so that the rope is gripped to a greater or lesser degree. However, these traction sheave grooves cannot be used for completely synthetic suspension ropes. With these synthetic fiber ropes the desired coefficient of friction can be effected very well by the material used, as for example polyurethane, polyamide or similar, and its hardness. However, deviations in the coefficient of friction due to manufacture, or unforeseeable reductions in the system coefficient of friction due to oil, lubricants, or other liquids, could permanently impair the tractive capacity. Under unfavorable conditions it can therefore not be ruled out that the rope moves without the drive being able to affect this movement which is undesirable.
The present invention relates to a traction system for synthetic fiber ropes that ensures a consistently good tractive capacity that is largely independent of environmental influences.
According to the present invention, at least part of the rope running surface of the rope drive element has a surface of roughness grade N7 to N12.
With the traction system according to the present invention, the range of the system coefficients of friction of the combination of rope surface and running surface of the rope drive element, as for example a rope pulley, traction sheave, rope drum, deflected drive belt, or similar, is much smaller. Tests by the applicant have shown that with a rope running surface according to the present invention, the system coefficient of friction in operation under normal conditions increases and advantageously stays constant at this higher level even if lubricants or other liquids become present.
The surface peak-to-valley height and/or the grain size of the coating are adapted to the Shore hardness of the rope sheath in such manner that by suitable combination in each case any requirement in respect of wear or function can be effected. To increase the service life of the rope sheath and to stabilize the long-term tractive capacity of the rope drive, for smaller peak-to-valley heights a friction material with a lower Shore hardness is used, whereas for higher Shore hardnesses synthetic materials with harder surfaces are used for the sheaths of ropes or covering layers of strands.
To achieve the advantages according to the present invention it is of no significance whether the synthetic fiber rope runs on a cylindrical surface of the rope drive element or in a shaped groove, as for example a semicircular groove. It is equally possible for there to be rope grooves with different shapes of profile, as for example a double semicircular groove, in which a complementary double or twin rope runs, etc. The advantages that can be achieved with the present invention are, in principle, also achieved irrespective of the shape selected for the rope running surface of the rope drive element.
As it runs over a traction sheave, the synthetic fiber rope adapts itself to the profile of the semicircular groove and under load deforms on the contact surface, or in the profiled groove, from its original circular shape to an oval section. According to the deformation, the specific pressures of the rope in the rope groove over the cross section of the groove are not constant but increase toward the base of the groove. This distribution of the specific pressures is more pronounced with a greater load on the rope.
In an advantageous preferred further development of the present invention in its embodiment with shaped grooves, the surface according to the invention is formed over parts of a groove and used to effect the distribution of the load-dependent specific pressure over the cross section of the shaped groove to adjust the tractive behavior of the rope and thereby to fulfil a desired functional requirement.
Taking an embodiment of the traction sheave according to the present invention with semicircular shaped grooves, in a first version the surface according to the invention is limited to an angular range of, for example, 45xc2x0 on the bed of the groove. The system coefficient of friction of this shape of groove is consequently high at the base of the groove and decreases toward the two sides. Correspondingly, the tractive behavior of a synthetic fiber rope running in this groove with no load on the rope is deliberately less pronounced than with a greater load acting on the synthetic fiber rope when the rope is pulled further into the shaped groove and lies on the bed of the groove with a maximum of specific pressure.
A second preferred exemplary embodiment of a shaped groove according to the present invention is to form the surface according to the invention symmetrically over two areas of the flanks of the cross section of the semicircular groove which are separated from each other. A load-dependent tractive behavior is also obtained with this embodiment. Here, in contrast to the exemplary embodiment previously described, the surface of the bed of the groove now has a lower peak-to-valley height. As a consequence, the traction of the heavily loaded synthetic fiber rope running in a semicircular groove formed in this way is less pronounced than that in the previous exemplary embodiment. On the other hand, the tractive behavior in the low load range is largely independent of the environmental influences.
In an advantageous third embodiment, the surface according to the invention is formed in an angular range of up to 140xc2x0 over almost the entire cross section of the groove. According to the invention, a synthetic fiber rope running in this shape of groove displays a high level of tractive behavior which is independent of the load on the rope and the environmental influences acting on it.
The surface according to the invention, which corresponds to a roughness average of Ra=1.6 to 50 xcexcm, can be obtained either by a mechanical finishing process suitable for creating a resistant surface texture, as for example knurling or similar, or else by coating the surface, preferably with corundum plasma.
Coating the rope running surface affords the additional possibility of subsequently converting conventional traction sheaves or rope drums for the advantageous tractive behavior with synthetic fiber ropes. The coating can either be applied to the desired areas on the steel groove or else appropriately flexible stiffeners are first plasma coated and then these pre-prepared plasma strips are attached to the desired point of the surface over which the rope runs by bonding with adhesive, fastening with screws, and/or some other means.
In a further development of the present invention the tractive behavior of a traction sheave with several shaped grooves formed in its circumference is systematically adapted to the selected requirements for the traction system by combining the embodiments of groove surfaces previously described.